The invention relates generally to displays and, in particular, to displays for producing three-dimensional images.
Displays presenting three-dimensional images are useful in a wide variety of applications. Prior techniques for such displays include the use of a lenticular lens to create a stereo image resulting in the illusion of depth. However, this system requires that the viewer be in a specific location to perceive the three-dimensional effect presented. Another technique is the use of two different colors or the use of opposite planes of polarization in the images to create the illusion of depth. However, the usefulness of both systems depends upon the viewer wearing special glasses.
Another technique for a three-dimensional display includes using a flat plate mirror for reflecting the images of a flat screen cathode ray tube back and forth along the Z axis (depth axis). This technique, better known as beamsplitting, typically uses a partially silvered mirror which passes some of the image and reflects some. The reflected image is displayed to the viewer as well as the passed image and an illusion of depth is created due to the optical pathlength differences between the images. In this technique, the viewer is confined to viewing the display within a relatively narrow angle from the depth or Z axis of the display, i.e., the axis which is perpendicular to the display screen and projects out of and into the screen. When the viewer moves out of that angle, the illusion of depth to the displayed object becomes distorted and eventually vanishes.
A further technique is the use of a flexible, circular, plastic plate mirror mounted on a circular rubber hinge to reflect the flat image of a cathode ray tube. The mechanical driving force moving the mirror toward and away from the viewer to give the illusion of depth is a low frequency audio speaker. Damping means for the mirror are used to tune it to the fundamental frequency. In many cases, the mechanics of the damping means become very complex and result in a complex, sensitive, and expensive system which is difficult to militarize. Also a system in accordance with this technique is relatively large since reflection is used.
A further problem in some three-dimensional display techniques is a lack of depth perception. In some cases, the viewer could not be sure if different objects were at the same or slightly different depths in the display.
Accordingly, it is an object of the invention to provide an improved display for presenting three-dimensional images of objects.
It is also an object of the invention to provide a three-dimensional display which can be viewed from a relatively wide angle without losing the depth dimension of the displayed image.
It is also an object of the invention to provide a three-dimensional display where the viewer does not need special hardware such as special glasses, to see the displayed three-dimensional image.
It is also an object of the invention to provide a three-dimensional display which is easier to construct and maintain, can be militarized, is relatively compact, and requires less special handling.